Electronically controllable compact display units find new and wider applications continuously. A well-known and a steadily growing field of applications can be found in stores and warehouses, where instead of conventional paper price labels on the shelves, the prices and other product related information is displayed using electronic shelf labels.
The electronic shelf label system, also known by the acronym ESL, is a system used by retailers for displaying product pricing on shelves. Typically, electronic shelf labels are implemented as electronic display modules that are attached to the front edge of retail shelving. These modules use different technologies to show the current product price and also other information to the customer. A communication network allows the price display to be automatically updated whenever a product price is changed. This automated system reduces pricing management labor costs and improves pricing accuracy.
ESL's are particularly suitable for use in large shops or supermarkets that offer thousands or tens of thousands product items for sale, whose prices must be updated frequently and correctly.
The electronic display modules can be updated from a centralized control sys-tem via wired or wireless communication. All-wired systems have obvious problems in terms of the layout limitations caused by complicated cabling due to the high number of individual ESL displays. Wireless systems have their major technological bottleneck in the need for individual power supplies for each ESL display unit and requirement for long power supply lifetime, i.e. operational life-time for the batteries. In addition, the wireless systems need to be able to pro-vide dependable communication channel in an environment that has high number of individual receiver-transmitter units that in order to prolong the battery life, need to operate with minimum transmitting power levels.
A display technology that is suitable for ESL applications is a so called Electronic Paper Display (EPD) that possesses a paper-like high contrast appearance, ultra-low power consumption, and a thin, light form. EPD's aim to give the viewer the experience of reading from paper, while providing the capability to electronically update the displayed information. EPD's are technology enabled, as one possibility, by electronic ink. Such ink carries an electrical charge enabling it to be updated through electronics. Electronic ink is well suited for EPD's as it is a reflective technology which requires no front or backlight, is viewable under a wide range of lighting conditions, including direct sunlight, and requires no power to maintain an image. Electrical power is only consumed when the displayed data is changed. In order become widely applied in different type of applications, wireless ESL's or corresponding electronically controlled wireless displays are faced with a number of requirements that are partly dictated by the manufacturing process and partly by the end use, for example, the use, environment and manageability in a store by the store personnel.
WO 0067110 (A1) (E Ink Corporation) discloses a display unit for electronic shelf price label system that utilizes electronic ink and EPD technology. The electronic display unit in WO 0067110 features a printable electronic display comprising an encapsulated electrophoretic display medium. The resulting electronic display is flexible and has in large measure the applications of a printed display. Further, since the encapsulated electrophoretic display medium used in the present invention can be printed, the display itself can be made inexpensively. The encapsulated electrophoretic display medium is an optoelectronically active material which comprises at least two phases: an electrophoretic contrast media phase and a coating/binding phase. The electrophoretic display medium can form, for example, a full color, multi-color, or two color (e.g. black and white) display. The electrophoretic phase comprises at least one species of encapsulated electrophoretic particles, having distinct physical and electrical characteristics, dispersed in a clear or dyed suspending fluid. The coating/binding phase includes a polymer matrix that surrounds the electrophoretic phase. In this embodiment, the polymer in the polymeric binder is capable of being dried, crosslinked, or otherwise cured as in traditional inks, and therefore a printing process can be used to deposit the encapsulated electrophoretic display medium onto a substrate.
In ESL's from the manufacturing point of view, in the order to achieve truly low cost ESL's, a roll-to-roll or web-based manufacturing process is preferred. This brings about severe limitations to the encapsulation of the ESL's to be suitable for such manufacturing methods, for example, due to the requirement a certain level of flexibility of the structures. Typically not all of the components required in an ESL and having cost and technical performance at acceptable level are nowadays available as mechanically flexible structures and this limitation would need to be somehow addressed in the manufacturing methods.
In order for the ESL's to be easily manageable during the manufacturing process and in the following logistical steps, the encapsulation of the ESL's need to provide a somewhat flexible structure against damage and preferably even thickness of the encapsulation or casing without any protruding or intending rims or order structures. Reasons for such requirements arise from, for example, simple and easy packaging and delivery of the items to the end user from the manufacturer, any preparations, automated or manual, needed for the ESL's to be used in the shelves (often also including adding conventional printed information on the ESL's) and installation/mounting of the ESL's on the shelves or holders therein. ESL's undergo a lot of handling during the preparation before they are installed to those substantially permanent final locations in the shelves. This make the requirements for these display modules clearly different from those of, for example, small sized electronic devices to be personally carried out in pockets etc. This also opens up more possibilities to choose materials as well in many cases relieves requirements for the size/dimensions of the devices. Further, the structure and encapsulation of ESL's need to be such that the wireless communication with the control systems can be realized with minimal or negligible interference from the encapsulation itself or by the surrounding structures, such as the metal shelves that the ESL's are to be attached to in the shop.
In addition, the preferred shape of the encapsulated devices in some applications is not a straight card type shape, but in order to improve the visual appearance and readability, the ESL display can also have a slightly curved shape so that the displayed information appears on the outwards curved surface. Further, in many applications the extreme thinness of the product might not be preferable, because it can complicate the handling of ESL's.
WO 2009103857 (A1) (Marisense Oy) discloses a layered thin display unit for ESL's comprising a flexible display layer having display material, preferably epaper, a flexible backplane layer having an electrode structure for driving the display material, a rigid component and a resilient layer. The unit is provided with wireless communication means including an antenna that is arranged in the backplane layer. This thin layered structure enables a roll-to-roll or web-based manufacturing process.
The main benefits of the display modules according to WO 2009103857 lie in the mechanical resistance of substantially thin and flexible display module laminates against mechanical impacts, as well as in the completely smooth outer surface and even thickness to aid overall manageability. Further, the encapsulation technique results in casings that have good performance in respect to the wireless communication using an internal antenna. A further benefit is the fact that the visual appearance of the ESL's resembles paper sheets or paper labels that are familiar for the customers and that can also be placed in the same type of holders, pockets or space as the conventional paper labels. It further allows using such energy source, for example, battery solutions, that provide long operational lifetimes without high cost that would be inherent for more exotic battery technologies.
The ESL's may, like in WO 2009103857, be implemented as semi-active RF tags that may be powered from incident RF communicating via modulated backscatter. The backscatter technique is relatively sensitive to interference form adjacent metal objects. As the ESL's are attached to shelves which often are of electric conducting material, typically metal, these metal shelves induce RF interference to the ESL's that are attached to them.